Aluminum is produced industrially by fused bath electrolysis in electrolytic cells according to the well-known Hall-Héroult process. French patent application FR 2 806 742 (corresponding to patent U.S. Pat. No. 6 409 894) describes installations of an electrolysis plant intended for the production of aluminum.
With the most widespread technology, electrolytic cells are provided with a plurality of “prebaked” anodes made of a carbonaceous material that are consumed during electrolytic reduction reactions of aluminum. The progressive consumption of anodes requires work on the electrolytic cells, particularly including the replacement of spent anodes by new anodes.
When changing an anode, in order to limit disturbance to the operation of an electrolytic cell, it is preferable to put the new anode into place such that its lower surface is at the same level as the other anodes in the cell.
It is known that it is possible to proceed as described below to determine the level of new anodes correctly. The rod of the spent anode is marked with a chalk-line at a location corresponding to a determined mark on the anode frame. The spent anode is extracted from the cell and is put down on a reference surface, typically a metallic plate. The level of the chalk-line on the rod is recorded, the spent anode is withdrawn, and a new anode is put into place on the reference surface. A chalk-line is drawn on the rod of the new anode at the recorded level. The new anode is put into place on the anode frame such that the chalk-line is at the same level as the determined mark on the anode frame. These essentially manual operations require action by an operator in the area in which the anode handling tools are being used, and expose the operator to the risks inherent to these operations such as risks of the load becoming detached, or liquid metal splashes.
It is also known that the anode handling tool can be fitted with a position sensor. In this case, the distance traveled by the tool when the spent anode being picked up is measured, the spent anode is put down on a reference surface, and the distance traveled by the tool at the time that the anode is supported on the reference surface is measured. The spent anode is withdrawn, a new anode is placed on the reference surface, and the distance traveled by the tool at the time that the anode is supported on the reference surface is measured. The difference between the last two measured distances is added to the first measured distance to determine the remaining distance that the handling tool should travel when the new anode is put into position in the electrolytic cell.
These different manners of working require multiple anode manipulations and displacement of the reference surface from one working area to another. The time spent on these operations considerably lengthens the durations of working cycles on electrolytic cells and the time period during which the hoods of pots remain open, which reduces the efficiency of collection means for effluents produced by electrolytic cells.
Therefore the applicant searched for a procedure and means of avoiding these disadvantages.